The preparation and properties of the C-doped modified layers on uranium surfaces by pulsed laser irradiating

摘要

The C-doped modified layer on uranium surface was prepared by pulsed laser irradiating in methane atmosphere. The microstructure of the obtained layer was characterised by X-ray diffraction (XRD), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The results show that the obtained layer is a composite layer with a gradual transition structure from UO2/free carbon to UO2-x/ UCxOy/free carbon to UC1-xOy/UC, and eventually to metallic U. To investigate the oxidation mechanism of the C-doped modified layer, initial oxidation behavior of O-rich surface and O-poor surface obtained after sputtering for 7 min and 60 min were studied by XPS. And the results illustrate that UCxOy with U4f(7/2) binding energy at 379.5 eV in the O-rich region is more resistant to oxidation than UC1-xOy/UC under oxygen exposure. Free carbon is distributed in the surface layer of C-doped modified layer prepared by pulsed laser irradiating, and the free carbon is also formed after oxidation of UC1-xOy, UC and UCxOy at room temperature. We speculate that the aggregation of free carbon increases the ability to prevent the inward diffusion of O atoms. Moreover, the results of the potentiodynamic polarization tests show that the C-doped modified layer improved the corrosion protective properties of metallic U. The self-corrosive potential and self-corrosive current of the C-doped modified layer are -1.47 x 10(-1) V vs. SCE and 9.46 x 10(-8) A/cm(2), respectively, while the values of metallic U are -5.67 x 10(-1) V vs. SCE and 8.08 x 10(-7) A/cm(2), respectively. (C) 2019 Elsevier B.V. All rights reserved.